Pipetting machine



Sept. 14, 1965 c. R. MENCKEN PIPETTING MACHINE Filed sept. 22, 1964 United States Patent O 3,206,072 PIPETTING MACHINE Calvin R. Mencken, Jessups, Md., assigner to the United States of America as represented by the Secretary of the Department of Health, Education, and Welfare Fired sept. 22, 1964, ser. No. 398,462 12 Claims. (Cl. 222-76) This invention relates to pipetting machines and aims generally to improve the same.

In a laboratory of physiology, for example, the procedure for the titration of serum antibody involves many dilferent dilutions of blood serum in a buered diluent. Tedious and time-consuming hand lpipetting has been required to make these dilutions. The volumes of diluent for each serum dilution are measured to the hundredth of a milliliter (ml.) in a range of from 0.01 to 1.00 ml., and each successive dilution may require an amount of diluent in any part of that range of volumes. Although there are several automatic pipetting machines available commercially, each of these requires a relatively complicated procedure for adjustment and recalibration to change the volume to be delivered.

Objects of the invention, severally and interdependently, are to provide a device of the character described capable of delivering diferent fluid volumes in the indicated range with a minimum of readjustment between deliveries; one which will expedite pipetting tasks such as that above mentioned; one sturdy enough for daily laboratory use; and one which will hold its calibration over long periods of time.

These and other objects and advantages of the invention will be apparent from the following description of an illustrative embodiment thereof, taken with the accompanying drawings, wherein:

FIG. l is a somewhat diagrammatic front elevation partly in section of the illustrative embodiment, with certain duplicated portions omitted for clarity, and showing in broken lines auxiliary equipment and .the location of the housing which surrounds parts of the apparatus in said embodiment;

FIG, 2 is a similarly diagrammatic plan view, partly broken away, of the embodiment of FIG. 1, with a corresponding broken line showing of the housing;

FIG. 3 is a schematic diagram of the electrical portions ofthe embodiment.

Referring to FIGS. l and 2, the pipettor comprises a syringe and valve portion A constituting a variable stroke positive displacement pump, and means B for selecting a predetermined stroke therefor corresponding to a predetermined amount of material to be pumped, and for operating the pump for delivering the quantity of material corresponding to the said selected stroke.

As is well shown in FIG. 1, the pump unit A comprises a pump chamber 10, a piston 11 reciprocable therein, suitable packing 12 for the piston, a check valved inlet passage 13 communicating with the chamber, a check valved outlet passage 14 also communicating therewith, a supply tubing 15 for connecting the inlet passage to a source vof supply of the liquid to be pipetteld, and a delivery tubing 16 for connecting the outlet passage 14 to a delivery tip, which may be a hypodermic needle or of any other suitable or usual form. The valved inlet passage 13 is preferably of relatively large crosssection. This provision assists in permitting a rapid back-stroke (suction stroke) of the piston 11, and avoids vaporization of volatile iluids in the syringe during such 3,206,072 Patented Sept. 14, 1965 lICC backstroke. The valved outlet passage or bore 14 communicates with the pump chamber 10 adjacent the top wall thereof, being flush therewith in the form shown. This feature minimizes or prevents the trapping of air in the syringe.

As is shown in broken lines in FIG. 1, a relief pressure standpipe, illustrated as a glass standpipe 17 extending to about the height of the pump chamber 10 and having a stoppered upper end and a T-connection at its bottom located in the supply line 15 between the syringe and the supply reservoir, is provided. This standpipe helps to prevent the development of a bumping or hammer effect during the stroke cycle which might tend to force liquid through the outlet valve at the end of the backstroke. The pump unit is detachably mounted on the base in any suitable manner, e.g. by thumb screws 18 attaching it to the pedestal 19 in the form shown. A detachable coupling 20 secures the -piston 11 to the piston drive rod 21 of the syringe operating unit B. Thus the entire liquid handling portion A of the apparatus can be quickly detached as a single unit for cleaning or sterilization.

The operating unit B to which the pump is connected by the coupling 20, is preferably enclosed in a casing or housing as indicated by the broken lines 22 in FIGS. 1 and 2. The operating keyboard and switches (indicated in FIG. 3) and any associated control or indicating elements, may be located on the top or front of the housing 22 which may be -sloped for convenience.

The means for selecting a predetermined stroke for the pump corresponding to a predetermined amount of liquid yto be delivered, in the form shown, comprises piston drive rod means 21, a pressure rod means 24 for advancing said drive rod, an anvil means 25, and a series of `selectable spacer means 25, 26a movable to overlie said anvil 25. The pressure rod means 24 has an abutment surface 2SV (FIG. l) positioned to `approach the anvil 25, as the pressure rod means advances the piston drive rod 21 and piston 11, until it engages the spacer means 26, 26a overlying the anvil 25, whereby the advancing stroke of -the piston is limited in accordance with the selected spacer means 26, 26a.

Stop means 30 is provided for limiting the retraction of the drive rod 21, shown as comprising a shoulder on the drive rod assembly which engages a wall of the supporting pedestal 31; and means 32 (FIG. 1), shown as a weak tension spring, is provided for elastically retracting the drive rod 21 to engage 'the stop means 30 as the pressure rod 24 is retracted. On the forward stroke the spring 32 is collapsed, and the pressure rod 24 directly engages the end of the piston drive rod 21.

The series of spacer means 26 consists of a set of studs of different callibrated width range carried circumferentially by a disc 35 rotatable ou an axis parallel to the direction of advance of the pressure rod 24, and resiliently movable along that axis. In the form shown the disc 35 is pinned to slidably mounted axle 36 mounted in the pedestals 31 and 37 and a spring 35A biases the shaft in the direction which moves the disc away from the anvil 25 so that it may be rotated to position anyof its studs in overlying relation to the anvil 25. When moved by the advance of the abutment surface 23, the carrier 35 and shaft 36 are shifted until the selected spacer 26 is supported against further movement by the anvil 25. The shaft 36 is rotated to position a selected spacer means 26 in overlying relation to the anvil by a chain drive 38 driven by a stepping switch means 40, of the twelve-position Ledex Rotary Stepping Relay type in the form shown.

In the form shown a plurality of the resiliently positioned carriers 35 and 35A are provided. The carrier 35A is carried by a sleeve 36A slidable on the shaft 36 and biased by a spring corresponding to the spring 36A, which may be a leaf spring or spring washer located between the discs 35 and 35A (not shown). The sleeve 36A is rotated to position a selected one of the series of studs 26A (similar respectively to studs 26, but ten times as widein the form shown), in overlying relation to the anvil 25 and the selected one of the studs 26. The sleeve 36A is rotated by a chain drive 38A driven by a stepping switch 40A (FIG. 2, omitted in FIG. 1 for clarity) which is of the same type as the stepping switch 40 in the form shown. Thus by appropriate control of the stepping switches 40 and 41 any number of units and decimal proportions thereof within the capacity of the apparatus may be selected for delivery. i The delivery of the selected quantity is effected by the resilient advancing of the pressure rod means 24 `until it is stopped by engagement with the selected spacer means 26, 26A overlying the anvil 25. The resilient advance of the pressure rod means 24 is effected by a driving motor 50 having a geared down output which drives the input portion of a magnetic clutch 51. The output portion of the clutch 51 drives an eccentric crank 52, which resiliently drives the pres-sure rod 24 via yan overriding spring linkage. The linkage in the form shown cornprises a pivoted fork 53 having a pin and slot connection to the pressure rod 24 and a pivoted arm 54 which is swung back and forth by a connecting rod 55 connecting it to the eccentric crank 52. The motion of the arm 54 is transmitted t the fork 53 via a spring 56 (FIG. 1). The arm 54 and fork 53 are connected by link 57 which has a pin and slot connection With one of them, and the spring 56 maintains maximum spacing between the arm and fork except when movement of the fork is arrested by the selected spacer means 26, 26A.

The wiring diagram of the illustrative embodiment iS shown in FIG. 3. Depression of one of the buttons of each bank 40 and 40A positions the corresponding spacers 26, 26A between the pressure rod 24 and the stop anvil 25. A trigger or start button C then activates the magnetic clutch 51, and the piston 11 is advanced and returned. At the end of this cycle a homing cam H (FIGS. 1 and 3) actuates a switch which deenergizes the magnetic clutch. A detent (not shown) or any other suitable means, may be provided to prevent over-ride past the nected to release the button TL to terminate such continuous actuation. An interlocking system is also included which prevents actuation of the clut-ch 51 while the control discs 35, 35A are in motion, and which prevents operation of the control discs 35, 35A while the clutch 51 is energized In more detail, referring to FIG. 3, the 4circuit of the illustrative embodiment comprises terminals 60 for connection to a 110 volt A.C. commercial power source. The current from terminals 60 is supplied via main switch 61 and fuses 62 to the motor 50 and to the power supply 63 for the controls, which comprises in the illustrative embodiment conventional rectilier and filter elements supplying about amperes of direct current at about 90 volts. The D C. supply is connected to the common input leads of the keyboard of selectors 40 and 40A. Depressing one of the decimal buttons in the key bank of stepping switch 40 energizes the correspondingly numbered side contact of the stepping switch, which steps until the open circuit portion of the stepping ring reaches and isolates ,the energized contact. The return leads from the ySteppers to the power supply are commoned at 65 and at 66 with a duplicate contact circuit interrupting and closing relay 67 interposed therein, the coil of the relay 67 being ar- `ranged in parallel with the magnetic clutch 51 for opening the return circuit of the stepping switches while the magnetic clutch is energized. Conversely, the return circuit of the magnetic lclutch 51 is provided with two slow release circuit in interrupting relay 68 and 68A the contacts of which are arranged in series, the coils of these relays being arranged in parallel respectively, with the loads of the respective stepping -switches 40, 40A, so that when either stepping switch is energized the return circuit of the magnetic clutch is interrupted. The feed circuit of the magnetic clutch is energized as follows: The trigger or starter button C, when closed energizes a two pole single throw relay D/ 2. One of its contacts D1 is a temporary holding contact and connects power from the back contact of the homing switch H to the coil D/Z to supply current to it until switch H is opened by the movement of the homing cam HC as the crank 52 is driven away from its home position. The other contacts D2 are temporary feeding contacts connected from the power supply to the magnetic clutch to energize the same until the homing cam HC releases the homing switch H to rest on its forward contact to maintain the energization of the magnetic clutch until the homing cam HC again shifts the switch I-I to its back contact. When the switch H leaves its back contact the holding current for the holding coil D/2 is interrupted and contacts D1 and D2 are opened. When switch H is again moved to its back contact the cycle is completed. Il 4the trigger or starter button C is kept closed, or shorted out by the trigger lock TL, then of course the relay D/Z remains energized and contacts D1 and D2 are kept closed until the trigger C or trigger latch TL is released, after which the cycle will be terminated by the homing switch H.

In the illustrative embodiment, the selector 40 selects the number of hundredths of a milliliter -to be delivered, from 0 to 9 hundredths, and the selector 40A selects the number of tenths of a milliliter to be delivered, from 0 to 10 tenths. The selectors are provided with capacitors 70 and arc Suppressors 71 for protecting the contacts thereof.

It will be appreciated that with the arrangement shown each time the trigger or starter but-ton C is touched, the piston will be operated to deliver the quantity of liquid which thas been selected -on the keyboards, and that such selected quantity can be altered at will at any time when the magnetic clutch 51 is not energized. Thus the speed and accuracy of pipetting are markedly increased.

While there have been described herein what are at present considered preferred embodiments of the various features of the invention, it will Ibe obvious to those skilled in the art that minor modifications and changes may be made without departing from the essence of the invention. It is therefore to be understood that the exemplary embodiments are illustrative and not restrictive of the invention, the scope of -Which is defined in the appended claims, and that all modifications that come wit-hin the meaning and range of equivalency of the claims are intended to be included therein.

The invention described herein is assigned to be Government of the United States and it is prayed that the present application be accorded fee exempt status in accordance with the opinion -of the Comptroller General No. B-lll, 648 (96 USPQ 453; 98 USPQ 238 and 607.01 MPEP).

A paper presenting details of the present invention, and of the characteristics of the operation thereof has been published by and with the consent of the applicant during the year next preceding the filing of the present application in the February 1964 issue of the Journal of Laboratory and Clinical Medicine, vol. 63, pages S25-331, which paper -is incorporated herein by reference.

I claim:

1. An automatic pipetting machine comprising, in combination,

(a) a variable stroke positive displacement pump,

(b) means for selecting a predetermined stroke therefor corresponding to a predetermined amount of ma- (4) said outlet passage communicating therewith terial to be pumped, and adjacent the top wall of said chamber for mini- (c) means for operating said pump for delivering the mizing trapping of air therein;

quantity of material corresponding to said selected (b) means for detachably supporting 'said pump;

stroke, 5 (c) means for selecting a predetermined stroke of wherein said selecting means comprises a piston drive said pump corresponding to a predetermined quantity rod and a pressure rod yfor advancing said drive rod, of material to be pumped, said selecting means coman anvil, and a series of selectable spacer means movprising able to overlie said anvil, said operating means com- (l) a piston drive rod detachably connected to prising means for advancing said pressure rod, said said piston for reciprocating the same pressure rod having an abutment surface positioned (2) a pressure rod for advancing said drive rod, to approach said anvil as said piston is advanced until said pressure rod comprising a first abutment it engages the spacer means overlying said anvil, surface,

whereby the advancing stroke of said piston is limf(3) an anvil affording a second abutment surface ited in accordance with the selected spacer means. facing said rst abutment surface,

2. A-combination according to claim 1, further compris- (4) a lirst disc rotatably mounted and carrying ing stop means for limiting the retraction of said drive peripherally thereona rst series of spacer means rod, and mean-s for elastically retracting said drive rod of different thicknesses and located to place a to said stop means as said pressure rod is retracted. vselected one of said lfirst series of spacer means 3. A combination according to claim 1, wherein a carbetween said abutment surfaces depending upon rier is provided for said series of spacer means, wherein the rotative position of said first disc, said carrier normally supports said spacer means out of (5) a second disc rotatably mounted and carrying contact with said anvil, and wherein said carrier is resilperipherally thereof a second series of spacer iently positioned and is movable by the pressure of said means of different thicknesses and positioned abutment surface against a spacer means carried thereby, to place a selected one of said second series of to bring said spacer means int-o contact with said anvil. spacer means between said abutment surfaces de- 4. A combination according to claim 3, wherein said pending upon the rotative position of said second carrier is a disc rotatable on an axis parallel to the direcdisc, tion of advance of said pressure rod, and resiliently mov- :(6) said rst and second discs being resiliently able along said axis. positioned on a common axis to present said S. A combination according to claim '3, wherein a pluspacer means in superposed but non-contacting rality of said resiliently positioned carriers are provided relation to said anvil and to each other, and each carrying a series of spacer means of a ditferent width being axially lmovable along said axis by engagerange and located to position a selected spacer means .nient of said first abutment surface therewith to of each of said plurality of carriers in overlying relation control the advance of said pressure rod, and to said anvil in superposed relation to each other, so that (7) stepping switch means for each of said discs the Sum 0f their thicknesses iS eEeCtiVe fOr limiting the mechanically coupled t0 drive the same t0 select advance stroke of said piston. the spacer means interposed between said abut- 6. A Combination according to Claim 1, Said means for ment surfaces, said stepping switch means each advancing said pressure rod compri-sing an eccentric crank, 4.0 comprising a quantity selector keyboard for cona connectin-g rod driven thereby, and an overriding spring trolling the stepping of said stepping switch linkage connecting said connecting rod to said pressure rod means to Selected positions `thereby to inter-pose and resiliently compressible by said connecting rod when correspondingly selected spacer means of said advance of said pressure rod iS Stopped by said Spaccr -rst and second series between said'abutment means. means,

7- A `ccIDbIliOI'i according 'i0 clalm 6, Sald Operating (d) means for operating said pump for delivering the means further comprising a driving motor, a magnetic quantity of material corresponding to said selected clutch for connecting said motor to drive said eccentric stroke, said operating means comprising crank, means for energizing said clutch, and means for '.(1) a reduction gear motor, deenergizing said clutch on completion of one full turn ,.)0 (2) means for supplying energy to continuously of said crank. t operate said motor,

8. A combination according to claim 3, said selecting (3) a driven Shaft having an eccentric crank, means comprising a Sonrcc ci electrical power, stepping r4) magnetic clutch means interposed between said switch means mechanically coupled to drive said carrier shaft and motor and energizable for driving Said means and a selector board for selecting the stopping posi- .Shaft from Said motor,

TOHO Sald StcPPlPg swltoh n leans- 2(5) an overriding spring linkage connected be- 9- A oomomoooo aoooromg to Claim o fufther oo m tween said eccentric crank and said pressure rod pnsmg means energlzod dunno Coil-ation 0i said Stepping for advancing the latter to the extent permitted gltghmls for inhlbiting operatlon of Sam pump Oper" by the spacer means interposed between said 10. A combination according t-o claim 8, further co-ml abutrgent Slirfaesf n. .d prising means energized during operation of said pump a rst .clrcult .or nerblzlqosm magnetlc operating means for inhibiting operation of said stepping clutch Sold first Cfrcult Compnsog two Sets of switch meanscontacts arranged in parallel therein and further 11. A combination according to claim 1t), further com- G- oontlcts affraogod m sonos therem: means for prising means energized during operation of said stepping o holding Said fufthcf ccl'l'f'flcts Open duflng OPcf" switch means for inhibiting operation of said pump operi011 '0f Sad Stepping Switches, a Start button fOr ating Hwang closing the tirst of said two sets of contacts, and

12. An automatic pipetting machine comprising means operable by rotation of said shaft for (a) a variable stroke positive displacement pump, said (a) closing the second said two sets of conpump comprising (1) a pump chamber, r(2) a piston reciprocable therein, (3) check valved inlet and outlet passages communicating with said pump chamber,

tacts and opening the first of said two sets of contacts when driving of said shaft has been initiated through energizing of said magnetic clutch via the rst of said two sets of contacts and said series contacts, and yfor 7 (b) 'opening the secon-d of said tw sets of contacts when said pressurel rod is re- H tracted, v

'(7) ser-ies contact means in the circuit of said stepping switches, and

I(8) means` energized by energization of said rst circuit lfor opening said series Contact means for preventing `operation of said stepping switches during energization of said magnetic clutch.

References Cited by the Examiner .UNITED STATES PATENTS 3,024,946 3/ 62 Forsyth Z22- 1309 X 3,081,913 3/63 Rotter Z22-43 X v3,097,763 7/6'3 Aluotto l222-43 3,134,508 5/64 Bayer etal Z22-309 X M. HENSON WOOD, JR., Primary Examiner. 

1. AN AUTOMATIC PIPETTING MACHINE COMPRISING, IN COMBINATION, (A) A VARIABLE STROKE POSITIVE DISPLACEMENT PUMP, (B) MEANS FOR SELECTING A PREDETERMINED STROKE THEREFOR CORRESPONDING TO A PREDETERMINED AMOUNT OF MATERIAL TO BE PUMPED, AND (C) MEANS FOR OPERATING SAID PUMP FOR DELIVERING THE QUANTITY OF MATERIAL CORRESPONDING TO SAID SELECTED STROKE, WHEREIN SAID SELECTING MEANS COMPRISES A PISTON DRIVE ROD AND A PRESSURE ROD FOR ADVANCING SAID DRIVE ROD, AN ANVIL, AND A SERIES OF SELECTABLE SPACER MEANS MOVABLE TO OVERLIE SAID ANVIL, SAID OPERATING MEANS COMPRISING MEANS FOR ADVANCING SAID PRESSURE ROD, SAID PRESSURE ROD HAVING AN ABUTMENT SURFACE POSITIONED TO APPROACH SAID ANVIL AS SAID PISTON IS ADVANCED UNTIL IT ENGAGES THE SPACER MEANS OVERLYING SAID ANVIL, WHEREBY THE ADVANCING STROKE OF SAID PISTON IS LIMITED IN ACCORDANCE WITH THE SELECTED SPACER MEANS. 